Recording materials which utilize electron-donating colorless dyes and electron-accepting compounds are well known Examples of such include pressure-sensitive recording paper, heat-sensitive paper, photo- and pressure-sensitive recording paper, electro thermo-recording paper, and the like. These recording materials are described in detail, e.g., in British Pat. No. 2,140,449, U.S. Pat. Nos. 4,480,052 and 4,436,920, Japanese Patent Publication No. 23922/85, Japanese Patent Application (OPI) Nos. 179836/82, 123556/85 and 123557/85 (the term "OPI" as used herein means an "unexamined published Japanese patent application"), and so on.
A heat-sensitive recording material must at least have the following properties: (1) it must produce a developed color images of sufficiently high density, (2) it must not cause coloration during storage before use, and (3) it must ensure sufficient fastness to the developed color images. However, heat-sensitive recording materials which adequately meet all of these requirements have not yet been obtained.
Addition of a benzotriazole compound, a hindered phenol compound or the like has been employed in order to 5 improve the fastness of developed color images. However, the improvement in fastness achieved by the addition of such a compound to a heat-sensitive recording material is still insufficient.